The drawing of an air bubble in the platinum filament,
which Edison observed under a microscope, is significant because it led him to
believe that he could increase the strength of the wire if he could remove the
bubbles. This, he reasoned, could be done if he kept the filament in an
evacuated bulb. He then developed a very efficient vacuum pump, which
later became critical for his experiments with carbon.

For more information about "the gang" at Menlo Park
see Pretzer, William S. (ed.), Working at inventing: Thomas A. Edison and the
Menlo Park Experience (Dearborn, MI: Henry Ford Museum and Greenfield
Village, 1989.